Method of reducing solid arcing product build-up between electrical contacts in pressurized fluid ambients

ABSTRACT

A method of substantially reducing the build-up of solid arcing products between contacts for making and breaking electrical circuits including the steps of adjusting the contacts to an arbitrary opening distance at which arcing will occur, placing the contacts in the dielectric fluid under greater than atmospheric pressure, opening and closing the contacts at a fixed operating circuit voltage to determine if the solid arcing product build-up forms, and readjusting the contact opening distance to minimize the value of the parameter (V/N)2/d where V is the operating circuit voltage, N is the number of sets (or pairs) of serially connected contacts and d is the distance between the contacts when in the fully open position. The value of the parameter may be further reduced by distributing V across a plurality of sets (or pairs) of such contacts connected in series and provided to be simultaneously actuated.

United States Patent [191 Pocock METHOD OF REDUCING SOLID ARCING PRODUCTBUILD-UP BETWEEN ELECTRICAL CONTACTS IN PRESSURIZED FLUID AMBIENTS [75]Inventor: Walter E. Pocock, Baltimore, Md.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC

[22] Filed: June 5, 1973 [21] Appl. No.: 367,254

Related US. Application Data [63] Continuation-in-part of Ser. No.316,778, Dec. 20,

[52] US. Cl 200/249, 29/622, 307/136, 307/137, 324/28 CB [51] Int. Cl.H01h 1/34 [58] Field of Search 200/166 CM, 144 R, 249; 307/136, 137;29/622, 630 C; 324/28 CB, 28

[56] References Cited OTHER PUBLICATIONS Peek et al., Fundamentals ofSwitching Relay Designs,

ADJUST CONTACTS TO ARBITRARY OPENING DISTANCE T PLACE CONTACTS INDIELECTRIC FLUID UNDER GREATER THAN ATMOSPHERIC PRESSURE OPEN AND CLOSECONTACTS AT OPERATING VOLTAGE READJUST CONTACTS TO MINIMIZE [1113,835,278 51 Sept. 10, 1974 Primary Examiner-Robert K. SchafferAssistant Examiner-William J. Smith Attorney, Agent, or Firm-R. S.Sciascia; Q. E. Hodges [5 7] ABSTRACT A method of substantially reducingthe build-up of solid arcing products between contacts for making andbreaking electrical circuits including the steps of adjusting thecontacts to an arbitrary opening distance at which arcing will occur,placing the contacts in the dielectric fluid under greater thanatmospheric pressure, opening and closing the contacts at a fixedoperating circuit voltage to determine if the solid arcing productbuild-up forms, and readjusting the contact opening distance to minimizethe value of the parameter (V/N)2/d where V is the operating circuitvoltage, N is the number of sets (or pairs) of serially connectedcontacts and d is the distance between the contacts when in the fullyopen position. The value of the parameter may be further reduced bydistributing V across a plurality of sets (or pairs) of such contactsconnected in series and provided to be simultaneously actuated.

6 Claims, 2 Drawing Figures PLURALITY OF SETS OF CONTACTSPATENIEDSEPIOIEIM SHEET 1 or 2 ADJUST CONTACTS TO ARBITRARY OPENINGDISTANCE OPEN AND CLOSE CONTACTS AT OPERATING VOLTAGE READJUST CONTACTSTO MINIMIZE DISTRIBUTE OPERATING VOLTAGE ACROSS A PLURALITY OF SETS OFCONTACTS FIG. i.

II ICS SILICONE LIQUID -o PROPRIETARY FLUID B (6.608) u MIL-H-6083CFLUID (zoos) IO 50 I00 CURRENT BEING INTERRUPTED, AMPERES METHOD OFREDUCING SOLID ARCING PRODUCT BUILD-UP BETWEEN ELECTRICAL CONTACTS INPRESSURIZED FLUID AMBIENTS 'the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION This invention relates generally to circuitmakers and breakers and more particularly to those of the mechanicaltype.

It was common, though notuniversal, practice on early deep submergencevehicles to put the bulk of the electrical switching gear inboard. Dueto increased power loads and the desirability of placing circuitinterrupting devices outside the pressure hulls of deep submersibles,there were two choices for protective housings for such devices. First,a hard shell enclosure filled with air or an inert gas under normalatmospheric pressure and built to withstand the external deep oceanpressure could be used. Second, a thin wall pressure compensated chamberfilled with a dielectric fluid could be used. In the thin wall chambers,the switching or circuit-interrupting device is immersed in thedielectric fluid and is subject to the pressure from the external oceanenvironment.

In the first case, the hard shell enclosures are disadvantageous in thatthey add bulk and weight which are critical factors in deep submergencevehicles. Also, the removal of heat from inside the hard shell and thetrapping of gaseous degradation products from the electrical insulationand other materials cause additional problems.

In the second case, the method is to immerse the electrical devices in afluid having good dielectric properties, in the pressure-compensatingchamber. The latter is a thin-walled enclosure of sufficientflexibility, or with a bellows attachment, to allow for compression ofthe fluid at the deep-ocean pressures. The fluids used or proposed foruse are either petroleum-derived or silicone liquids having a specificgravity less than 1.0, thus providing a measure of buoyancy.

A number of unexpected electrical contact failures oncircuit-interrupting devices occurred in these early applications. Solidproducts, later identified as carbon in the case of petroleum-derivedfluids and carbon plus silica (silicon dioxide, SiO in the case ofsilicones, which has resulted from arcing in the fluids during circuitinterruption, had bridged the contacts, causing a short circuit in theopen position. The objectionable deposits were dubbed clinkers. Thesefailures, which were not too clearly understood, and for which there wasno prospect of an immediate solution, caused an understandable reactionamong those involved in designing and operating deep submersibles. In atleast one case, it was decided to use hard shell enclosures for housingcircuit-interrupting equipment on a vehicle then in the planning stage.This approach involves other problems, notably a large increase inweight, sealing and making penetrations through the enclosure, and poorheat dissipation from the equipment inside the hard shell.

To date, various stock circuit interrupting devices have been developed,sometimes with design modification for operation in fluids on deepsubmersibles, often with highly unsatisfactory results. At one time,there were considerable doubts about using pressure compensating fluidsbecause of the history of failure. However, the advantages of bulk andweight savings, few or no penetration problems, and good heat transfermake this an attractive approach.

SUMMARY OF THE INVENTION In accordance with this invention, contactfailure problems in circuit interrupting devices can be overcome, makingthe pressure compensating fluid approach not only practical but probablythe preferred direction to take. It has been found, in accordance withthis invention, that the build-up of solid arcing products betweencontacts of a circuit interrupter in dielectric fluids under greaterthan atmospheric pressure can be substantially reduced by a method ofminimizing the value of the parameter (V/N)/a where V is the operatingcircuit voltage, N is the number of sets (or pairs) of seriallyconnected contacts, and d is the distance between the contacts when inthe fully open position.

STATEMENT OF THE OBJECT OF THE INVENTION Accordingly, the primary objectof this invention is to provide a method of substantially reducing thebuildup of solid arcing products between contacts in dielectric fluidunder greater than atmospheric pressure;

It is also an object of this invention to reduce such build-up byminimizing the value of the parameter (V/N)/a' where V is the operatingcircuit voltage, N is the number of sets of serially connected contactsand d is the distance between the contacts when in the fully openposition.

It is a further object of this invention to reduce such build-up byadjusting the opening distance to determine a suitable opening distancenecessary to substantailly reduce the solid arcing product build-upbetween the contacts; and

It is still a further object of this invention to reduce the value ofthe parameter by distributing V across plural sets of such contactsconnected in series and provided to be simultaneously actuated.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustrationof the method of this invention.

FIG. 2 shows the maximum value of the parameter (V/N)/d for no contactfailure by clinker formation, for fluids of three different viscosities.

DESCRIPTION OF THE PREFERRED EMBODIMENT A study of the behavior ofcircuit-interrupting devices was first made. At atmospheric pressure,contact failure seemed always to occur by erosion due to repeatedarcing, usually within 10,000 to 40,000 interruptions. Under the sameconditions, except at pressures of 1,000 psi or greater, failureoccurred readily by clinker formation, which correlated with thefailures observed on deep-diving vehicles. The following additionalobservations were made:

Contact failure in fluids under pressure by clinker formation oftenoccurs in fewer than interruptions.

Contact life under pressure (stated as the number of interruptions tofailure) decreases with:

increasing open-circuit voltage;

increasing current;

increasing fluid viscosity; and

increasing pressure.

The failure of contacts under pressure depends not only on the amount ofsolid product formed but also on how readily it deposits between thecontacts in preference to dispersing in the fluid. This is believed tobe related to the formation of bubbles of gaseous are breakdownproducts. At atmospheric pressure the motion of the bubbles tends tosweep the solid particles from the contact zone and causes them todisperse in the fluid. At higher pressures the bubbles are smaller anddenser and therefore slower moving, or they may not form at all becauseof their solubility in the fluid at high pressure. Thus thesolids-dispersing action is lost. It has also been suggested thatelectrical charges on the particles, under the influence of theelectrical field of the opening contacts, may partially account for thebridging of the contacts by the solids. The clinker in one case, formedby interrupting I00 amperes at 120 volts dc, in 1 cs silicone fluid at13,500 psi, has been tentatively identified as a mixture of silica andcarbon. The silica (white in color) completely coats the outside of thedeposit, which, when broken open, is seen to have a core of carbon. Thismay very well indicate the migration of charged carbon and silicaparticles in opposite directions.

Among the various factors that have been investigated in relation to theclinker failure problem, two controllable variables appear to be highlycritical in their effect on contact life. The first of these is thevoltage across the contacts when completely open. For a particular setof contacts, in a given dc circuit, in a given medium (gaseous orliquid) and at a fixed current, the energy of the circuit-interruptingarc falls off sharply as open-circuit voltage is decreased. This is 5seen in the data of Table 1.

TABLE 1 Are Energy Versus Open-Circuit Voltage at Constant Current, forThree Values of Pressure in 1 cs Silicone Fluid When the voltage ishalved, the are energy decreases to one-fourth of its original value orless. Thus, are energy variesas the square of the open circuit voltage,or greater. It has already been stated that contact life under pressuredecreases with increasing open-circuit voltage. The magnitude of thisdecrease is also fairly large for agiven increase in voltage. It is notcertain,

however, that voltage affects contact life only by virtue of its effecton are energy.

It can be seen that in going from, say a 60-volt to a -volt system on avehicle, the problem of electrical contact failure inpressure-compensating fluids increases sharply. The principle justdiscussed can be utilized by designing circuit-interrupting devices withmultiple sets of contacts in series. Ideally, if all the sets ofcontacts opened simultaneously, the total voltage would be distributeduniformly over the individual sets during the arcing process. Thus,using a device having four sets in series in a 120 volt circuit, thevoltage per set of contacts would be 30 volts. In practice, the contactsdo not open exactly simultaneously, and the resistance across the arcitself varies from one set of contacts to another; but it has been shownthat a very good approach to the ideal condition can be made without theneed of highly critical adjustments. There is, of course, a practicallimit to the number of sets of contacts that can be used in seriesbeyond which the weight and size of the device increase out ofproportion to the benefits obtained. For applications being consideredhere, with maximum voltages of 120 volts and maximum currents of 500amperes in normal operation, four or possibly six sets are felt to be areasonable limit based on experience thus far.

Control of the parameter (V/N)/a has been found to have a significanteffect in lessening the tendency of clinker failure. Such control may beaccomplished by controlling the operating voltage at the are betweeneach set of contacts.

The second controllable variable that is highly critical in its effecton contact life under pressure is contact spacing, that is, the spacebetween contacts in the fullopen position. The typical effect is seen inthe data of Table 2.

TABLE 2 Effect of Contact Spacing on Contact Life, in 1 cs SiliconeFluid, 13,500 psi, 120 volts dc, at Two Current Values Contact ContactLife, Number Test Current Spacing, of Interruptions to Run Ampereslnches Clinker Failure 1 0.13 10 2 10 0.19 1080 3 0.25 10.000 (nofailure) 4 0.13 5 S 25 0.19 1750 6 0.25 10,000 (no failure) at 13,500psi pressure, for three liquids. This parameter is that below whichcontact failure would not be expected; that is, for a given value ofcurrent for each of the three fluids no contact failure would be ex-.pected for all values of (V/N)/a' below the curve corresponding to thatfluid. Since clinker formation decreases w hss r s tis prsss raautsharia? ftqm 13.500psi (which corresponds to the maximum forejusting thecontacts to an arbitrary opening distance at which arcing will occur,placing the contacts in the dielectric fluid, under greater thanatmospheric pressure, opening and closing the contacts at a fixedoperating circuit voltage to determine if the solid arcing productbuild-up forms, and readjusting the contact opening distance to minimizethe value of the paramter (V/N)/d where V is the operating circuitvoltage, N is the number of sets of serially connected contacts and d isthe distance between the contacts when in the fully open position. Thevalue of the parameter may be further reduced by distributing theoperating circuit voltage V across a plurality of sets of such contactscon- TABLE 3 Observed Versus Predicted Performance of Four ProprietaryContactors Breaking DC Loads Proprietary Number of Contact LiquidContactor Contact Breaks Contact Opening in Designa- Estimated SpacingSpeed Which Predicted Observed tion Actual 'Equivalent inches in/secOperated Performance Performance A 4 2 0.36 11.5 in MlL-l-l- 10,000inter- 20,000 inter- 1 cs 6083C ruptions withruptions withsilicone fluidout failure at out failure at at 120 volts & 120 volts, 13,500 currentfrom 200 amp. psi 5 to 300 amp.; 13,500 psi 13,500 psi ressure B 2 1.50.076 2.1 in Propria. 5000 "E? a. 5000 inter- 1 cs etary ruptionswithruptions withsilicone Fluid out failure at out failure at at A V &current 60V, 120A; 13,500 from 5 to 50A; 9000 psi. psi 13,500 psi. b.Clinker b. Rapid failure in 5 clinker interruptions failure at V at120V, 120A; or greater & 9000 si. any current cv Clinker 5A; 13,500failure in 422 psi. interruptions at 120V, 25A; 9000 psi.

C 2 1.5 0.11 Not Propria. 5000 inter- 5000 inter- Measetary ruptionswithruptions withured Fluid out failure at out failure at A 60V &current 60V, A;

from 5 to 4,500 psi 200A;

13,500 psi.

b. Rapid clinker failure at 120V & any

current 5A;

D 4 2 0.085 1.7 1 cs Winter a. Clinker silicone ruptions withfailure inout failure at interruptions V & current at 120V, 50A;

13,500 psi b. 5000 interruptions without failure at 80V, 95A; 13,500psi.

The value of N for each contactor was an estimated equivalent number ofcontact breaks.

This number was based on a visual observation of the arc distributionover the individual contacts, made at atmospheric pressure. Theestimated equivalent was in all cases less than the actual number ofbreaks because arcing, and therefore voltage, was not equally dividedover the individual breaks. Contact opening speed is included in thetable, since it may be of interest.

The present method of substantially reducing the build-up of solidarcing products between electrical' contacts at a given operatingvoltage in dielectric fluids under greater than atmospheric pressureincludes adviscosity, clinker formation can be reduced by using a,

fluid of lower viscosity. That is, where it is impractical or impossibleto change the number of contacts or their gap, a fluid of lowerviscosity can be substituted to decrease clinker formation.

If a number of sets of contacts, or contact breaks, in

series are opened simultaneously, the circuit voltage is theorecticallydistributed substantially equally over the individual sets of contacts.The ideal condition of all the sets of contacts opening exactlysimultaneously is not likely in practice and therefore the reduction inare energy will not be as great as desired. However, the ideal conditioncan be approached to a highly useful degree in that a partialdistribution of voltage among the multiple breaks and a lowering of arcenergy are obtained. A good criterion of satisfactory arc distributionon a multi-break contactor has been found to be the appearance ofvisible arcing at all breaks during contact opening, even though theintensities of the individual arcs may be unequal.

In the selection or design of a contactor, the basic features such as:single versus double pole, single versus double throw, latching circuitsversus spring return of armatures, and normally open versus normallyclosed contacts, are determined primarily by the requirements of thecircuit. Substantially equally distributing the circuit voltage acrossthe plural sets of contactors necessitates either using a plurality ofsinglepole contactors, or a single device having a plurality of poles. Aplurality of single-pole contactors will not be satisfactory since theircontacts may not open simultaneously, or nearly simultaneously, so thatthe possible benefit of the multiple breaks is not obtained.Furthermore, the critical factors of total bulk and weight of aplurality of single-pole contactors may be considerably more than thatof a single multiple pole device. Therefore, a single multiple poledevice is preferred.

In operation, the method of this invention includes the steps ofadjusting the contacts to an arbitrary opening distance therebetween;placing the contacts in the dielectric fluid under greater thanatmospheric pressure; opening and closing the contacts at the operatingcircuit voltage thereacross to determine if the solid arcing productbuild-up forms therebetween; and readjusting the contact openingdistance to determine a suitable opening necessary to substantiallyreduce the solid arcing product build-up between the contacts. Thismethod may be further enhanced by reducing the voltage across thecontacts by distributing the circuit voltage across plural sets of suchcontacts in series provided to be simultaneously actuated. Such contactsmay be made adjustable as to their opening distance by any number ofknown means such as may be adapted to suit the type of contacts beingused.

As has been stated, the use of electrical contacts in a dielectric fluidunder pressure than atmospheric pressure is known, but, the gist of thepresent invention lies in the reduction of the build-up of solid arcingproducts between such contacts due to control of the parameter (V/N)/asuch that the value of the parameter may be minimized either byadjusting the opening distance d between the contacts and/or bydistributing the circuit voltage V across plural sets of simultaneouslyactuated contacts.

Obviously many modifications and variations of the method of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the appended claimsthe invention may be practiced otherwise than as specifically described.

What is claimed is:

I. In an electrical circuit immersed in a dielectric fluid capable ofproducing solid particles as a result of arcing between contacts, saidcircuit comprising a source of voltage V and a plurality N of sets ofserially connected contacts having a contact gap of d inches, the methodof reducing the formation of solid particles between the contacts whichcomprises: reducing the value of the parameter (V/N)/d below apreselected maximum for a given current flow, fluid pressure, and fluidviscosity.

2. The method of claim 1 wherein said reduction includes the step ofincreasing the plurality N of sets of serially connected contacts.

3. The method of claim 1 wherein said reduction includes the step ofincreasing the contact gap d.

4. In an electrical circuit immersed in a dielectric fluid of viscositya capable of producing solid particles as a result of arcing betweencontacts, said circuit comprising a source of voltage V and a pluralityN of sets of serially connected contacts having a contact gap of dinches, the method of reducing the formation of solid particles betweenthe contacts which comprises: reducing the viscosity p. of the fluidsuch that the value of the parameter (V/N)/a is less than a preselectedmaximum for the new viscosity at a given fluid pressure and currentflow.

5. An electrical circuit immersed in a dielectric fluid capable ofproducing solid particles as a result of arcing between contactscomprising:

a source of voltage V and a plurality N of sets of serially connectedcontacts having a contact gap d, said contact gap d being chosen to makethe value of the parameter (V/N)/d less than a preselected maximum for agiven current flow fluid pressure, and fluid viscosity.

6. An electrical circuit immersed in a dielectric fluid capable ofproducing solid particles as a result of arcing between contactscomprising:

a source of voltage V and a plurality N of sets of serially connectedcontacts having a contact gap d, said plurality N being chosen to makethe value of the parameter (V/N)/d less than a preselected maximum for agiven current flow fluid pressure,

and fluid viscosity.

1. In an electrical circuit immersed in a dielectric fluid capable ofproducing solid particles as a result of arcing between contacts, saidcircuit comprising a source of voltage V and a plurality N of sets ofserially connected contacts having a contact gap of d inches, the methodof reducing the formation of solid particles between the contacts whichcomprises: reducing the value of the parameter (V/N)/d2 below apreselected maximum for a given current flow, fluid pressure, and fluidviscosity.
 2. The method of claim 1 wherein said reduction includes thestep of increasing the plurality N of sets of serially connectedcontacts.
 3. The method of claim 1 wherein said reduction incLudes thestep of increasing the contact gap d.
 4. In an electrical circuitimmersed in a dielectric fluid of viscosity Mu capable of producingsolid particles as a result of arcing between contacts, said circuitcomprising a source of voltage V and a plurality N of sets of seriallyconnected contacts having a contact gap of d inches, the method ofreducing the formation of solid particles between the contacts whichcomprises: reducing the viscosity Mu of the fluid such that the value ofthe parameter (V/N)/d2 is less than a preselected maximum for the newviscosity at a given fluid pressure and current flow.
 5. An electricalcircuit immersed in a dielectric fluid capable of producing solidparticles as a result of arcing between contacts comprising: a source ofvoltage V and a plurality N of sets of serially connected contactshaving a contact gap d, said contact gap d being chosen to make thevalue of the parameter (V/N)/d2 less than a preselected maximum for agiven current flow fluid pressure, and fluid viscosity.
 6. An electricalcircuit immersed in a dielectric fluid capable of producing solidparticles as a result of arcing between contacts comprising: a source ofvoltage V and a plurality N of sets of serially connected contactshaving a contact gap d, said plurality N being chosen to make the valueof the parameter (V/N)/d2 less than a preselected maximum for a givencurrent flow fluid pressure, and fluid viscosity.